acm multimedia october 4, 2001 real-time voice communication over the internet using packet path...
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ACM MultimediaOctober 4, 2001
Real-time Voice Communication over the Internet Using Packet Path Diversity
Yi Liang, Eckehard Steinbach, and Bernd Girod
Image, Video, and Multimedia Systems GroupInformation Systems LaboratoryDepartment of Electrical EngineeringStanford University
Liang, Steinbach, Girod: Real-time Voice Communication over the Internet Using Packet Path Diversity 2
Overview
Requirements of VoIP
Packet path diversity for low delay VoIP
Adaptive multi-stream playout scheduling
Internet experiments
Demo
Liang, Steinbach, Girod: Real-time Voice Communication over the Internet Using Packet Path Diversity 3
Requirements of VoIP
Small end-to-end delay for conversational services ( <150ms ) Delay variations (jitter) have to be smoothed using receiver buffer Late packets are lost, no time for retransmissions Small residual packet loss rate is ok Trade-off between end-to-end delay and late loss rate
Sender
Receiver
Playout
Time
1 2 3 4 5 6 7 8
1 2 3 4 5 6 7 8
Missed deadlineReceiver buffer
Time
TimePacketization
time
Liang, Steinbach, Girod: Real-time Voice Communication over the Internet Using Packet Path Diversity 4
Motivation for Packet Path Diversity for VoIP In up to 80% better alternative path
[Savage ‘99] Multi-path routing [Sidhu ‘91, Bahk ‘92] Uncorrelated packet loss on independent
paths [Apostolopoulos ‘01] Efficiency of FEC limited by packet loss
and delay correlation [Bolot ‘93, Bolot ‘99] Delay jitter is the major killer of delay
sensitive applications Our contributions:
Exploitation of statistically independent jitter behavior for VoIP
Adaptive multi-stream playout scheduling technique
R
S
Secondpath
1 2
Speech
Packet Path Diversity
Default path
Liang, Steinbach, Girod: Real-time Voice Communication over the Internet Using Packet Path Diversity 5
Two-path speech coding
Redundant description of voice stream (MDC) Two bitstreams for two paths
Stream 1: [Jiang 2000] Even samples: (8-bit, PCM) Odd samples: (2-bit, ADPCM)
Stream 2: Vice versa 25% Overhead Loss of one packet small reduction in speech quality Loss of both packets error concealment
Es1
s2
O E O E O
O E O E O E
E O
Packet length
Time
Liang, Steinbach, Girod: Real-time Voice Communication over the Internet Using Packet Path Diversity 6
Packet Path Diversity for Low Delay VoIP
Time1 2 3 4 5 6
Sending on path 1
Receiving on path 1
Packet Path Diversity reduces effective delay jitter and therefore late loss rate
Packet Path Diversity reduces effective delay jitter and therefore late loss rate
Playout1 2 3 4 65
1 2 3 4 5 6Sending on path 2
Receiving on path 2
Liang, Steinbach, Girod: Real-time Voice Communication over the Internet Using Packet Path Diversity 7
Adaptive Playout Scheduling
Adaptive playout scheduling and speech scaling allow us touse more packets for playout at given mean target delay
Adaptive playout scheduling and speech scaling allow us touse more packets for playout at given mean target delay
Time1 2 3 4 5 6Sending on path 1
Receiving on path 1
1Constant Playout
stretching compressing
Adaptive Playout1 2 3 4 65
If past delay values indicate congestion delay playout of next packet(s) by stretching speech signal
If past delay values are small advance playout of next packet(s) by compressing speech signal
2 3 4 65
Liang, Steinbach, Girod: Real-time Voice Communication over the Internet Using Packet Path Diversity 8
Modification of Playout Speed Based on time-domain interpolation algorithm WSOLA
[Verhelst et al., 1993, Liang 2001]
Output packet
1/20/1 2/3 3 4
Original packet
Pitch-period
0 21 3 4
Template
Liang, Steinbach, Girod: Real-time Voice Communication over the Internet Using Packet Path Diversity 9
Adaptive Two-stream Playout Scheduling
1
2
1 1 2 2 1 2 2 1
Pr |
Pr |
ˆ ˆ ˆ ˆ ˆ ˆ( (1 ) (1 ))
i i iplay play
iplay
iplay
C d both descriptions lost d
only one description lost d
d p p p p p p
playout deadlineplayout deadline
estimate of loss probabilityestimate of loss probability
1p̂
Histogram of past delay values
Combination of Packet Path Diversity and Adaptive Playout Minimization of Lagrangian cost function
Delayiplayd
Variation ofiplayd
Liang, Steinbach, Girod: Real-time Voice Communication over the Internet Using Packet Path Diversity 10
QwestQwest
Internet Experiment
Explicit path selection using relay server [Apostolopoulos ‘01] UDP packets with payload of 240 bytes
Exodus
Comm.
Exodus
Comm.
BBN PlanetBBN Planet
Netergy Networks
192.84.16.176MIT
18.184.0.50
Harvard140.247.62.110
(5ms)(45ms)
(40ms) (5ms)
(5ms)Sender
Relay Server
Receiver
Liang, Steinbach, Girod: Real-time Voice Communication over the Internet Using Packet Path Diversity 11
Measured Packet Delay Trace
Delay in ms
Packet number
Liang, Steinbach, Girod: Real-time Voice Communication over the Internet Using Packet Path Diversity 12
Adaptive Two-stream Playout Scheduling
Delay in ms
Packet number
Liang, Steinbach, Girod: Real-time Voice Communication over the Internet Using Packet Path Diversity 13
Comparison: Single-path Transmission with FEC
2 3 41 1 2 3
2 41 1 3
2 3 41
Stream received with packet loss
Stream reconstructed
3
Stream sent
Packets protected with FEC
FEC: adds redundancy by sending one or more copies of the source signal in the following packet(s) [Bolot ‘96]
FEC protected single-stream
For fair comparison
Primary copy: quantized at fine resolution (8-bit)
Secondary copy quantized at coarser resolution (2-bit)
Same data rate as transmission with Packet Path Diversity
Same adaptive playout scheduling technique
Liang, Steinbach, Girod: Real-time Voice Communication over the Internet Using Packet Path Diversity 14
Results
delay (ms)
Packet loss ratein %
Liang, Steinbach, Girod: Real-time Voice Communication over the Internet Using Packet Path Diversity 15
Demo
Original
Average total end-to-end delay: 84 ms Error concealment: speech segment repetition
Average total end-to-end delay: 84 ms Error concealment: speech segment repetition
Path Diversity Single-stream with FECat same data rate
Liang, Steinbach, Girod: Real-time Voice Communication over the Internet Using Packet Path Diversity 16
Conclusions Packet Path Diversity for real-time voice communication over IP
Multiple Description Coding of speech signal Quality improves with each description received
Exploitation of statistically independent jitter behavior Improvement of delay versus speech quality trade-off
Adaptive Playout Scheduling Flexible playout deadline using time-scale modification Reduction of late loss rate for given target delay Lagrangian cost function for two-path transmission
Internet experiments Implementation of path diversity using relay server Observation of largely independent delay jitter behavior Significant speech quality improvement in comparison to single-path
transmission with FEC at the same data rate and end-to-end delay
Liang, Steinbach, Girod: Real-time Voice Communication over the Internet Using Packet Path Diversity 17
PESQ Results
Perceptual Evaluation of Speech Quality (ITU-T Rec. P.862, Feb. 2001)
PESQ can be used for end-to-end quality assessment
Ranges from –0.5 to 4.5 but usually produces MOS-like scores between 1.0 and 4.5
Liang, Steinbach, Girod: Real-time Voice Communication over the Internet Using Packet Path Diversity 18
Internet Experiment II
VBNS IP Backbone
Service
VBNS IP Backbone
ServiceDANTE
Operations
DANTE Operations
UUNET
Tech.
UUNET
Tech.
Erlangen131.188.130.136
Harvard140.247.62.110(7ms)
(40ms)
AT&TAT&T
(5ms)(5ms)
(10ms)
New Jersey165.230.227.81
Path 1 (direct): N. J. – Erlangen Path 2 (alternative): N. J. – Harvard – Erlangen
Liang, Steinbach, Girod: Real-time Voice Communication over the Internet Using Packet Path Diversity 19
Result
Path 1 (direct): N. J. – GermanyPath 2 (alternative): N. J. – Harvard –
Germany
Mean delay
61.3/65.0 ms link loss
0.6% / 1.1% Significant reduction of
late loss and end-to-end delay by packet path diversity
Liang, Steinbach, Girod: Real-time Voice Communication over the Internet Using Packet Path Diversity 20
Constant Playout
Trade-off between packet loss and delay
Constant playout deadline
late loss
Liang, Steinbach, Girod: Real-time Voice Communication over the Internet Using Packet Path Diversity 21
Adaptive playout deadline
Adaptive Playout
Adaptation to delay variation (jitter)
Liang, Steinbach, Girod: Real-time Voice Communication over the Internet Using Packet Path Diversity 22
Late Loss Mean Delay
Liang, Steinbach, Girod: Real-time Voice Communication over the Internet Using Packet Path Diversity 23
Speech Scaling
Liang, Steinbach, Girod: Real-time Voice Communication over the Internet Using Packet Path Diversity 24
Demo 2
Original
Average total end-to-end delay: 108 msAverage total end-to-end delay: 108 ms
Path Diversity(PESQ: 4.1)
Single-stream with FEC(PESQ: 3.5)
Liang, Steinbach, Girod: Real-time Voice Communication over the Internet Using Packet Path Diversity 25
Voice over IP (VoIP)
VoIP is rapidly growing 900% 1998-1999 5000% 1999-2004
2004
1999
1998
135 billion minutes
2.7 billion minutes
310 million minutes
[Source: IEEE Spectrum, Mai 2000]
Liang, Steinbach, Girod: Real-time Voice Communication over the Internet Using Packet Path Diversity 26
Limits of Speech Stretching
More than 25% is annoyingMore than 25% is annoying
Original Stretching: s=1.3
Liang, Steinbach, Girod: Real-time Voice Communication over the Internet Using Packet Path Diversity 27
Speech and Audio Scaling
Speech scaling
Audio scaling
original stretched: s=1.3 compressed: f=0.7
original stretched: s=1.3 compressed: f=0.7